Apparatus and method of preparing and delivering a fluid mixture using direct proppant injection

ABSTRACT

An apparatus and method for preparing and delivering a fluid mixture. The apparatus includes a high pressure differential solids feeder assembly and a pressurized mixing apparatus. The feeder assembly is coupled to a proppant storage vessel at ambient pressure and receives a continuous unpressurized proppant output flow from the proppant storage vessel. The feeder assembly is configured to output a continuous pressurized proppant output flow of sufficient mass to achieve continuous operation of the apparatus in an uninterrupted episode for an individual fracture stage. The pressurized mixing apparatus is coupled to the feeder assembly and in fluidic communication with the continuous pressurized proppant output flow and a continuous pressurized fracturing fluid flow. The pressurized mixing apparatus is configured to output a continuous flow of a pressurized fluid mixture of a sufficient volume and mass to achieve continuous operation of the apparatus in an uninterrupted episode for the individual fracture stage.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 14/624,531, filed on Feb. 17, 2015, now US Publication 20150204166A1, which is a Continuation-in-part of U.S. application Ser. No. 13/689,873, filed on Nov. 30, 2012, now abandoned, both of which are hereby incorporated by reference in their respective entireties.

BACKGROUND

Embodiments disclosed herein relate generally to an apparatus and method of delivering a fluid mixture (i.e., slurry) into a wellbore in an uninterrupted episode for each fracture stage design.

Hydraulic stimulation or fracturing, commonly known as hydrofracking, or simply fracturing, is a technique used to release petroleum, natural gas or other substances for extraction from underground reservoir rock formations. A wellbore is drilled into the reservoir rock formation, and a treatment fluid is pumped which causes fractures and allows for the release of trapped substances produced from these subterranean natural reservoirs. Current wellbore fracturing systems utilize a process wherein a slurry of a fracturing fluid and a proppant (e.g. sand) is created and then pumped into the well at high pressure. When water-based fracturing fluids are used, the proppant, water and appropriate chemicals can be mixed at atmospheric pressure and then pumped up to a higher pressure for injection into the well.

This type of hydraulic stimulation, utilizing water-based fracturing fluids, is usually undertaken in multiple fracture stages or episodes. Stimulation of each individual fracture stage utilizes a specific fluid volume and proppant mass per stage and, due to the ability to operate and hold these materials under ambient conditions, each fracture stage is able to be conducted in one uninterrupted episode. Subsequent to completion of one fracture stage, a subsequent fracture stage is commenced utilizing another specific fluid volume and proppant mass to comprise the slurry, and the process repeats.

At present, the desire in the industry is to stimulate using fluids other than water, and more specifically liquefied or dense phase supercritical gases, but maintaining the same fluid volumes and proppant mass per fracture stage that is used for today's known water stimulation methods. With the use of these alternate fluids, the stimulation of each individual fracture stage is still desirably sought to be accomplished in an uninterrupted episode for each fracture stage. However, when fluids other than water (e.g. liquid CO₂ or liquid propane) are used as the fracturing fluid, these fluids must be kept at a sufficient pressure throughout the hydraulic fracturing system to avoid undesired vaporization. As a result, the blending of these fracturing fluids with proppant, chemicals, etc., to form the fracturing slurry, must also be accomplished while the fluids are kept under a sufficiently high pressure. Current pressurized blenders, or mixing apparatus exist, for this purpose but with limitations.

Known pressurized blenders capable of blending these vaporizing fracturing fluids with the proppant at a suitably high pressure typically utilize a pressurized proppant storage vessel to feed and meter the proppant into the pressurized fracturing fluid. These known pressurized blenders require pre-loading with the entire desired mass of proppant to be utilized during a given fracture stage. After loading, the entire mass of proppant is maintained under pressure within the blender. The pressurized proppant storage vessels are typically single lock hopper configurations having a capacity in the range of 20-40 tons of proppant (e.g., sand). However, typical fracture stage designs employ 125,000-250,000 lbs. or more of proppant for each stage of fracturing. Due to volume limitations, a single known pressurized lock hopper and pressurized blender assembly would only able to pump a fraction of the complete fracture stage design. To provide the required large proppant mass, multiple lock hopper configurations may be utilized to deliver the desired fracture stage design with proppant and additional fracturing fluids.

In addition, the limited volume capacity of known pressurized proppant storage vessel systems provides for limited amounts of proppant to be blended with the fracturing fluid. If the fracturing design requires more sand, then multiple pressurized proppant storage vessels must be used. This adds to the complexity and capital expenditures of the fracturing system. In addition, known pressurized blenders require an undesirably long elapsed time to reload them with proppant for the next fracture stage. In some instances, some pressurized blender operations require the blender unit be moved off-site to another location for the purpose of reloading with proppant, also requiring an undesirably long time and potentially adding to the truck traffic associated with fracturing operations. In many instances, the limited capacity requires specialized logistics and on-pad (or off-pad) proppant handling equipment to be used in conjunction with the pressurized proppant storage vessel system.

Accordingly, there is a need for an improved pumping system and method for delivering the alternate fracturing fluids (e.g., liquid CO₂ or liquid propane), and more particularly a fracturing slurry, into a wellbore that will enable the blending and pumping of essentially unlimited quantities on an uninterrupted basis of proppant and alternate fracturing fluid to form the fluid mixture. The ability to deliver unlimited quantities will provide for continuous operation of the pressurized blender and sand feeding equipment in an uninterrupted episode throughout each fracture stage, maintain the same desired total fluid volume and proppant mass for each individual fracture stage in each uninterrupted episode, enable fracture plans to be based upon reservoir stimulation requirements without imposing equipment constraints, and therefore providing overall a more efficient hydraulic fracturing system.

BRIEF SUMMARY

These and other shortcomings of the prior art are addressed by the present disclosure, which provides an apparatus and method of preparing and delivering a fluid mixture using direct proppant injection to a pressurized mixing apparatus.

In accordance with an embodiment, provided is an apparatus for preparing and delivering a fluid mixture. The apparatus includes a high pressure differential solids feeder assembly coupled to a proppant storage vessel at an ambient pressure and a pressurized mixing apparatus coupled to the high pressure differential solids feeder assembly. The high pressure differential solids feeder assembly includes a proppant inlet in fluidic communication with a proppant flow at the ambient pressure. The high pressure differential solids feeder assembly is configured to output a continuous pressurized proppant output flow of a sufficient mass to achieve continuous operation of the apparatus in an uninterrupted episode for an individual fracture stage. The continuous pressurized proppant output flow is output at a mixing pressure, wherein the mixing pressure is greater than the ambient pressure. The pressurized mixing apparatus is coupled to the high pressure differential solids feeder assembly. The pressurized mixing apparatus includes at least one inlet in fluidic communication with the continuous pressurized proppant output flow and a continuous pressurized fracturing fluid flow. The pressurized mixing apparatus is configured to mix the continuous pressurized proppant output flow and the continuous pressurized fracturing fluid flow therein and output a continuous flow of a pressurized fluid mixture of proppant and fracturing fluid of a sufficient volume and mass to achieve continuous operation of the apparatus in an uninterrupted episode for the individual fracture stage. The continuous flow of the pressurized fluid mixture of proppant and fracturing fluid is output at or above the mixing pressure.

In accordance with another embodiment, provided is an apparatus for preparing and delivering a fluid mixture. The apparatus includes a proppant storage vessel, a high pressure differential solids feeder assembly, a fracturing fluid storage vessel, a pressurized mixing apparatus and a pump assembly. The proppant storage vessel is configured to contain therein a proppant material and output a proppant output flow at ambient pressure. The high pressure differential solids feeder assembly is coupled to the proppant storage vessel. The high pressure differential solids feeder assembly includes a proppant inlet in fluidic communication with the proppant output flow. The high pressure differential solids feeder assembly is configured to output a continuous pressurized proppant output flow of a sufficient mass to achieve continuous operation of the apparatus in an uninterrupted episode for an individual fracture stage. The continuous pressurized proppant output flow is output at a mixing pressure, wherein the mixing pressure is greater than the ambient pressure. The fracturing fluid storage vessel is configured to contain therein a fracturing fluid and output a continuous pressurized fracturing fluid output flow at a mixing pressure, wherein the fracture mixing pressure is greater than the ambient pressure. The pressurized mixing apparatus is coupled to the high pressure differential solids feeder assembly. The pressurized mixing apparatus including at least one inlet in fluidic communication with the continuous pressurized proppant output flow and the continuous pressurized fracturing fluid flow. The pressurized mixing apparatus is configured to mix the continuous pressurized proppant output flow and the continuous pressurized fracturing fluid flow therein and output a continuous flow of a pressurized fluid mixture of proppant and fracturing fluid of a sufficient volume and mass to achieve continuous operation of the apparatus in an uninterrupted episode for the individual fracture stage. The continuous flow of the pressurized fluid mixture of proppant and fracturing fluid is output at or above the mixing pressure. The pump assembly is coupled to the pressurized mixing chamber and configured to deliver the pressurized fluid mixture therein to a downstream component at an injection pressure, wherein the injection pressure is greater than the mixing pressure.

In accordance with yet another embodiment, provided is a method of preparing and delivering a fluid mixture. The method including providing a continuous proppant output flow at ambient pressure into a high pressure differential solids feeder assembly configured to output a continuous pressurized proppant output flow of a sufficient mass to achieve continuous operation of the apparatus in an uninterrupted episode for an individual fracture stage, wherein the continuous pressurized proppant output flow is output at a mixing pressure, wherein the mixing pressure is greater than the ambient pressure; inputting the continuous pressurized proppant output flow and a continuous pressurized fracture fluid output flow at the mixing pressure and of a sufficient volume to achieve continuous operation of the apparatus in an uninterrupted episode for an individual fracture stage, into a pressurized mixing apparatus; and mixing the continuous pressurized proppant output flow and the continuous pressurized fracturing fluid output flow therein the pressurized mixing apparatus and outputting a continuous pressurized flow of a fluid mixture of proppant and fracturing fluid of a sufficient volume and mass to achieve continuous operation of the apparatus in an uninterrupted episode for the individual fracture stage, wherein the continuous flow of the pressurized fluid mixture of proppant and fracturing fluid is output at or above the mixing pressure.

Other objects and advantages of the present disclosure will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The above and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein

FIG. 1 is a schematic diagram of an apparatus for delivering a fluid mixture using a high pressure differential solids feeder assembly for direct proppant injection to a pressurized mixing apparatus constructed in accordance with an embodiment;

FIG. 2 is a schematic diagram of a portion of the apparatus of FIG. 1 including a feeder assembly and pressurized mixing apparatus constructed in accordance with an embodiment;

FIG. 3 is a schematic diagram of an apparatus for delivering a fluid mixture using a Continuous solid feed pump assembly for direct proppant injection to a pressurized mixing apparatus constructed in accordance with another embodiment;

FIG. 4 is a schematic diagram of an apparatus for delivering a fluid mixture using a eductor pump assembly direct proppant injection to a pressurized mixing apparatus constructed in accordance with still another embodiment;

FIG. 5 is a schematic diagram of an apparatus for delivering a fluid mixture using a pressurized rotary positive displacement pump assembly for direct proppant injection to a pressurized mixing apparatus constructed in accordance with still another embodiment; and

FIG. 6 is a schematic block diagram of a method of delivering a fluid mixture using a direct proppant injection to a pressurized mixing apparatus constructed in accordance with still another embodiment.

DETAILED DESCRIPTION

This disclosure will be described for the purposes of illustration only in connection with certain embodiments; however, it is to be understood that other objects and advantages of the present disclosure will be made apparent by the following description of the drawings according to the disclosure. While preferred embodiments are disclosed, they are not intended to be limiting. Rather, the general principles set forth herein are considered to be merely illustrative of the scope of the present disclosure and it is to be further understood that numerous changes may be made without straying from the scope of the present disclosure.

Preferred embodiments of the present disclosure are illustrated in the figures with like numerals being used to refer to like and corresponding parts of the various drawings. It is also understood that terms such as “top”, “bottom”, “outward”, “inward”, and the like are words of convenience and are not to be construed as limiting terms. It is to be noted that the terms “first,” “second,” and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity).

As used herein, the process of forming of a fluid mixture includes mixing a fluid with a powdered or particulate material, such as proppant, a powdered dissolvable or a hydratable additive (prior to hydration). The fluids are handled as continuous fluid streams over an uninterrupted episode for each fracture stage.

Referring to the drawings wherein, as previously stated, identical reference numerals denote the same elements throughout the various views, FIG. 1 depicts in a simplified block diagram, elements of an apparatus 100 for preparing and delivering a continuous fluid mixture (slurry) of solids (proppant) and liquefied gas, including direct proppant injection to a pressurized blender, or mixing apparatus, including sufficient fluid volume and proppant mass so as to achieve an uninterrupted episode for each individual fracture stage to achieve the desired fracture stage design, according to an embodiment.

The apparatus 100 includes a proppant storage vessel 102 coupled to a high pressure differential solids feeder assembly 104 at an inlet 106 of the high pressure differential solids feeder assembly 104. The proppant storage vessel 102 includes an outlet 108 configured in fluidic communication with the inlet 106 of the high pressure differential solids feeder assembly 104. The proppant storage vessel 102 is configured as a traditional unpressurized storage type vessel and includes a body 110 configured to hold a proppant material 112 therein at atmospheric pressure, also referred to herein as ambient pressure. In an embodiment, the proppant storage vessel 102 may be configured including an open top and configured to hold the proppant material 112 therein at atmospheric pressure. In an embodiment, the proppant storage vessel may be configured including a closed top and configured to hold the proppant material 112 therein at atmospheric pressure. The proppant storage vessel 102 may further include a proppant material inlet 114 coupled to a proppant material loading device 116 and a source of proppant material (not shown). In an embodiment, the proppant material 112 may be comprised of sand, ceramic proppant, a mixture thereof or other material utilized as proppant in hydraulic fracturing operations. The proppant storage vessel 102 provides adequate storage and loading capabilities to allow for a supply of proppant material 112 to the high pressure differential solids feeder assembly 104 sufficient to achieve continuous operation of the apparatus 100 in an uninterrupted episode for an individual fracture stage.

During operation, the proppant storage vessel 102 may be loaded by the material loading device 116, such as a screw auger, conveyor, or any other means configured to move the proppant material 112 from a proppant supply source (not shown) to the proppant storage vessel 102. Alternate means for providing the proppant material 112 to the proppant storage vessel 102 are anticipated herein. The proppant storage vessel 102 is configured to hold the proppant material 112 therein at atmospheric pressure and thus enables loading/recharging during operation of the remaining system components.

The high pressure differential solids feeder assembly 104 includes a pump assembly capable of receiving a continuous proppant output flow 118 at atmospheric pressure via outlet 108 of the proppant storage vessel 102 and the inlet 106 of the high pressure differential solids feeder assembly 104. The high pressure differential solids feeder assembly 104 is further configured to provide at an outlet 120, a continuous pressurized proppant output flow 122 at a mixing pressure, wherein the continuous pressurized proppant output flow 122 is of a sufficient mass flow to provide continuous operation of the apparatus 100 in an uninterrupted episode for each individual fracture stage. The mixing pressure at which the continuous pressurized proppant output flow 122 is discharged is greater than the ambient pressure. In an embodiment, the mixing pressure is in a range of about 50 psi to 400 psi, and preferably at a pressure of approximately 300 psi.

A pressurized blender, or mixing apparatus, 124 is configured to receive the continuous pressurized proppant output flow 122 via a proppant inlet 126. A pressurized fracturing fluid storage vessel 128 is provided in fluidic communication via an outlet 130 with a fracturing fluid inlet 132 of the pressurized mixing apparatus 124. The fracturing fluid storage vessel 128 is configured for storage of a fracturing fluid 134 at a required temperature and storage pressure, and more particularly at or above the mixing pressure. The pressurized mixing apparatus 124 is configured to receive a continuous pressurized fracturing fluid output flow 136 at the mixing pressure via the inlet 132, wherein the continuous pressurized fracturing fluid output flow 136 is of a sufficient volume to provide continuous operation of the apparatus 100 in an uninterrupted episode for each individual fracture stage.

During operation, the continuous pressurized proppant output flow 122 and the continuous pressurized fracturing fluid output flow 136 are blended, or mixed, within the pressurized mixing apparatus 124 at the mixing pressure. Subsequent to mixing, the pressurized mixing apparatus 124 provides a continuous fluid mixture output flow 138, previously referred to herein as a slurry, to a high pressure fracturing fluid (slurry) pump assembly 142, via an outlet 140, wherein the continuous fluid mixture (slurry) output flow 138 is sufficient to provide continuous operation of the apparatus 100 in an uninterrupted episode for each individual fracture stage. In alternate embodiments, a fracture fluid (slurry) booster pump 141 may be provided inline between the mixing apparatus 124 and the high pressure fracturing fluid (slurry) pump assembly 142, or alternatively provided as part of the functionality of the high pressure fracturing fluid (slurry) pump assembly 142. The continuous fluid mixture (slurry) output flow 138 is output at the mixing pressure. The continuous fluid mixture (slurry) output flow 138 is received via a fluid mixture inlet 144 of the high pressure pump assembly 142. The high pressure fracturing fluid (slurry) pump assembly 142 is configured to deliver the continuous fluid mixture (slurry) output flow 138 received therein to a downstream component 146 at an injection pressure, wherein the injection pressure is greater than the mixing pressure. More specifically, in an embodiment, the high pressure fracturing fluid (slurry) pump assembly 142 is configured to deliver a continuous high pressure fluid mixture (slurry) output flow 148 via an outlet 150 of the high pressure fracturing fluid (slurry) pump assembly 142 to an inlet 152 of the downstream component 146, such as a well head 154, wherein the continuous high pressure fluid mixture (slurry) output flow 148 is of sufficient volume and mass to provide continuous operation of the apparatus 100 in an uninterrupted episode for each individual fracture stage.

Referring more specifically to FIG. 2, illustrated is a portion of the apparatus 100 of FIG. 1 as indicated by dotted line in FIG. 1. More particularly, illustrated in FIG. 2 are the high pressure differential solids feeder assembly 104 and the pressurized mixing apparatus 124. The inclusion of the high pressure differential solids feeder assembly 104 in apparatus 100 provides unlimited amounts of the proppant material 112 to be continuously blended with the pressurized fracturing fluid 134, using conventional sand logistics and on-pad handling equipment. The high pressure differential solids feeder assembly 104 is capable of operating continuously in uninterrupted episodes throughout each fracture stage, in contrast to semi-batch operating modes of the state of the art lock hoppers, whereby the proppant must be batch pressurized in a mixing apparatus with multiple lock hopper cycles or multiple lock hopper configurations required to deliver sufficient output flow for similar desired fracture stage designs.

As illustrated in FIG. 2, the high pressure differential solids feeder assembly 104 separates the low pressure inlet, and more particularly the inlet 106 from the high pressure outlet, and more particularly the outlet 120. This separation enables transport of the bulk solids (proppant) from the low pressure inlet 106 to the high pressure discharge area 120 on a continuous, uninterrupted basis while simultaneously preventing a flow of the pressurized fracturing fluid 134, via the fracturing fluid output flow 136, back to the inlet 106. In contrast to known lock hopper designs that may include a valve configured to intermittently open and close to create separation of pressure zones, the high pressure differential solids feeder assembly 104 provides for an uninterrupted solids flow at both the inlet 106 and the outlet 120, simultaneously. In an embodiment, while some degree of high pressure fluid backflow may occur through the high pressure differential solids feeder assembly 104, the device 104 is configured to actively manage such back flow (e.g., active venting).

In an embodiment, the high pressure differential solids feeder assembly 104 may be a continuous solid feed pump assembly, such as a Posimetric® pump assembly, (described presently) that employs positive-displacement action to provide precise flow control and positive metering of the unpressurized proppant material output flow 118 into the pressurized mixing apparatus 124, a screw auger, conveyor, or any other similar means (described presently) configured to move the unpressurized proppant material output flow 118 into the pressurized mixing apparatus 124, an eductor pump assembly (described presently) that employs the Venturi effect to convert pressure energy of a motive fluid to velocity energy to feed the unpressurized proppant material output flow 118 into the pressurized mixing apparatus 124, or a rotary-type pump (i.e., a rotary valve) that employs positive-displacement action to feed the unpressurized proppant material output flow 118 into the pressurized mixing apparatus 124.

In an embodiment the pressurized mixing apparatus 140 is configured as a tank that provides for mixing of contents therein in response to agitation or in response to static mixing utilizing plates and/or mixer elements that provide for mixing in response to turbulence and/or mixing of a plurality of flow paths generated in the flow.

In an embodiment, the integration of the high pressure differential solids feeder assembly 104 with the pressurized mixing apparatus 140 may include coupling the outlet 120 of the high pressure differential solids feeder assembly 104 to a gas headspace (not shown) of the pressurized mixer apparatus 140. In addition, in an embodiment, the pressurized mixer apparatus 140 may employ a small retention volume so as to allow for faster change-overs between proppant sizes and types.

Further embodiments of an apparatus for delivering a pressurized fluid using continuous direct injection of a proppant at ambient pressure into a pressurized mixing apparatus, of a sufficient volume and mass to provide continuous operation of the apparatus 100 in an uninterrupted episode for each individual fracture stage, are illustrated in FIGS. 3-5. More particularly, illustrated are alternate embodiments of the high pressure differential solids feeder assembly 104 as described in FIGS. 1 and 2. Each of the embodiments of FIGS. 3-5 addresses the direct delivery of a dry proppant material, such as proppant material 112 of FIG. 1, to a pump assembly for pressurization and subsequent mixing with the fracturing fluid 134 in a pressurized mixing apparatus 124. Utilizing a dry proppant material obviates the need for additional fluid for wetting, thereby simplifying the process and required equipment and removing costly and potentially flammable (e.g., hydrocarbon) wetting agent(s). Each of the embodiments of FIGS. 3-5 describes a pump assembly that may be utilized for the high pressure differential solids feeder assembly 104, as described in FIGS. 1 and 2. Accordingly, like numbers are used to identify like elements throughout the described embodiments and in an effort to provide a concise description of these embodiments, like features and elements previously described will not be further described.

Referring more specifically to FIG. 3, illustrated is an embodiment of an apparatus for delivering a continuous, uninterrupted fluid mixture, generally referenced 200. The apparatus 200 includes a proppant storage vessel 102 configured to contain therein an unpressurized proppant material 112 and output a continuous unpressurized proppant output flow 118 at ambient pressure. A high pressure differential solids feeder assembly 104 is provided and coupled to the proppant storage vessel 102. The high pressure differential solids feeder assembly 104 includes a proppant inlet 106 in fluidic communication with the unpressurized proppant storage vessel proppant output flow 118. In this particular embodiment, the high pressure differential solids feeder assembly 104 is a continuous solid feed pump assembly 202. The continuous solid feed pump assembly 202 employs positive-displacement action to feed the unpressurized proppant material output flow 118 without the need for a pressurizing fluid, into the pressurized mixing apparatus as a continuous flow sufficient to provide continuous operation of the apparatus 200 in an uninterrupted episode for each individual fracture stage. In this particular embodiment, the continuous solid feed pump assembly 202 does not employ screws, augers, belts or vibratory trays to convey the unpressurized proppant material output flow 118 and in contrast employs at least one vertical rotating spool 204 disposed within a pump body 208 to move the proppant material 112 therein. The continuous proppant output flow 118 is initially input at an input 106 that is coupled to the pump body 208. As the continuous proppant output flow 118 enters and fills the pump assembly 202, and more particularly the pump body 208, from above, the material locks itself firmly into the confines of the rotating spool 204 contained therein, which carries it through an arc of approximately 180°. More particularly, the continuous proppant output flow 118 is rotated within the rotating spool 204, housed within the pump body 208, where it becomes “locked up” or compacted so as to act as a solid mass, and discharged via an output duct 210 at the outlet 120 as a continuous pressurized proppant output flow 122 of sufficient mass to provide continuous operation of the apparatus 200 in an uninterrupted episode for each individual fracture stage. While within the pump body 208, the proppant material 118 acts as a solid mass and a seal against the high pressure outlet 120. At the time of discharge via the outlet 120, the continuous pressurized proppant material output flow 122 is output at an increased pressure, and more particularly at a mixing pressure that is higher than ambient pressure.

In a preferred embodiment, the continuous solid feed pump assembly 202 is configured as a rotary displacement pump assembly 203, and includes a consolidation section 212, a rotating section 214 and a discharge section 216. During operation, the unpressurized proppant material output flow 118 enters the pump assembly 202 and becomes consolidated as the individual proppant material particles settle and come into contact with each other as well as the sidewalls defining the pump body 208, the particles become compacted and act as a solid mass and form a seal against the high pressure outlet environment. As the unpressurized proppant material output flow 118 rotates in the rotating spool 204 and pump body 208, the pressure of the proppant material output flow 118 is increased, forming the continuous pressurized proppant output flow 122. Discharge of the continuous pressurized proppant output flow 122 at the increased mixing pressure occurs upon rotating of the rotating spool 204 to the outlet 120. Exemplary pump assemblies are described in commonly assigned U.S. Pat. No. 8,006,827, D. Aldred et al., “Transporting Particulate Material”, issued Aug. 3, 2011, which is incorporated by reference herein in its entirety.

The continuous solid feed pump assembly 202 is configured to output the continuous pressurized proppant output flow 122 at the mixing pressure, wherein the mixing pressure is greater than the ambient pressure. The apparatus 200 further includes a fracturing fluid storage vessel 128 configured to contain therein a fracturing fluid 134 and output a continuous pressurized fracturing fluid output flow 136 at or above the mixing pressure, of a sufficient volume to provide continuous operation of the apparatus 200 in an uninterrupted episode for each individual fracture stage. A pressurized blender, or mixing apparatus, 124 is coupled to the continuous solid feed pump assembly 202 to receive the discharged continuous pressurized proppant output flow 122. The pressurized mixing apparatus 124 is additionally coupled to the pressurized fracturing fluid storage vessel 128 to receive the discharged continuous fracturing fluid output flow 136 therefrom. The mixing apparatus 124 is configured to mix the continuous pressurized proppant output flow 122 and the continuous pressurized fracturing fluid output flow 136 therein and output a continuous output of a fluid mixture (slurry) 138 of proppant and fracturing fluid, at the mixing pressure, and of a sufficient volume and mass to provide continuous operation of the apparatus 200 in an uninterrupted episode for each individual fracture stage to deliver the proppant mass and fluid volume desired by the fracture stage design. A fracturing fluid (slurry) booster pump 141 and a high pressure fracturing fluid (slurry) pump assembly 142 are coupled to the mixing apparatus 124 and configured to receive the continuous output of a fluid mixture (slurry) 138 and deliver a continuous flow of a high pressure fluid mixture (slurry) 148 therein to a downstream component 146 at an injection pressure and in an amount sufficient to provide continuous operation of the apparatus 200 in an uninterrupted episode for each individual fracture stage. The injection pressure of the continuous flow of a high pressure fluid mixture (slurry) 148 is at or greater than the mixing pressure.

Referring more specifically to FIG. 4, illustrated is another embodiment of an apparatus 300 for delivering a continuous flow of a high pressure fluid mixture (slurry) of a sufficient volume and mass to provide continuous operation of the apparatus 300 in an uninterrupted episode for each individual fracture stage as desired by the fracture stage design. The apparatus 300 includes a proppant storage vessel 102 configured to contain therein a proppant material 112 and output a continuous proppant output flow 118 at ambient pressure. The apparatus 300 further includes a fracturing fluid storage vessel 128 configured to contain therein a pressurized fracturing fluid 134 and output a continuous pressurized fracturing fluid output flow 136 at or above a mixing pressure, wherein the mixing pressure is greater than the ambient pressure as previously described. A high pressure differential solids feeder assembly 104 is provided and coupled to the proppant storage vessel 102 and the fracturing fluid storage vessel 128. The high pressure differential solids feeder assembly 104 includes a proppant inlet 106 in fluidic communication with the proppant storage vessel continuous proppant output flow 118 and a fracture fluid inlet 324 in fluidic communication with at least a portion of the continuous pressurized fracturing fluid output flow 136. In this particular embodiment, the high pressure differential solids feeder assembly 104 is an eductor pump assembly 302. During operation, the eductor pump assembly 302 employs the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid, and more particularly a portion of the continuous fracturing fluid output flow 136, to velocity energy to feed the proppant material 112. Similar to the previously described continuous solid feed pump assembly 202, the eductor pump assembly 302 does not employ screws, augers, belts or vibratory trays to convey the proppant material 112 within the pump assembly toward the downstream components.

As illustrated in FIG. 4, the continuous proppant output flow 118 is initially input into the eductor pump assembly 302 via an input duct 306 that is coupled to a pump body 308. The input of the continuous proppant output flow 118 may be metered by a valve mechanism (not shown) disposed in the input duct 306. In an embodiment, the eductor pump assembly 302 further includes a first converging nozzle 310, a second converging nozzle 312, a mixing chamber 314 and a diffuser, or expansion feature, 316.

In an embodiment, the eductor pump assembly 302 includes the eductor body 308, and more particularly a suction chamber 318 that is driven by the motive fluid, and more particularly at least a portion of the continuous fracturing fluid output flow 136 utilized as a motive flow. In an embodiment, at least a portion of the continuous fracturing fluid output flow 136 is input directly into the pressurized mixing apparatus 124. The continuous fracturing fluid output flow 136 is accelerated through the first converging nozzle 310. As with traditional eductors, accelerating a higher pressure fluid through the first converging nozzle 310 drops the static pressure of a motive flow exiting through the first converging nozzle 310, while simultaneously decreasing the static pressure within the suction chamber 318. The lower suction pressure in the suction chamber 318 draws in the continuous proppant output flow 118, as a suction flow via the inlet port 106 of the eductor pump assembly 302. Subsequently, a continuous flow of a fluid mixture 320 of a sufficient volume and mass to provide continuous operation of the apparatus 300 in an uninterrupted episode for each individual fracture stage, comprised of a combination of the continuous proppant output flow 118 and the continuous pressurized fracturing fluid output flow 136, is delivered to the second converging nozzle 312 prior to reaching the mixing chamber 314. The fluid mixture 320, comprised of the continuous proppant output flow 118 and the continuous pressurized fracturing fluid output flow 136, is further mixed within the pressurized mixing chamber 314 as the stratifications between the two fluids are allowed to settle out and as the turbulent fluid structure is reduced. The continuous flow of the fluid mixture 320 exiting the mixing chamber 314 is expanded in the expansion feature 316, prior to being delivered to the downstream components that may ultimately be in fluidic communication with a wellhead. The expansion feature 316 provides an expansion of the fluid mixture 320 and provides a decrease in the velocity of the fluid mixture 320 and recovery of the pressure of the fluid mixture 320 allowing the fluid to be delivered to a pressurized mixing apparatus 124 in a continuous flow, at the mixing pressure, and a sufficient volume and mass to provide continuous operation of the apparatus 300 in an uninterrupted episode for each individual fracture stage to deliver the proppant mass & fluid volume desired by the fracture stage design.

During operation of the apparatus 300, including the eductor pump assembly 302, the eductor pump assembly 302 is placed in operation by pressurizing the suction chamber 318. Subsequent to the appropriate pressure condition being reached, an optional valve mechanism, or gate, 322, disposed between the proppant storage vessel 102 and the inlet port 106 may be opened to allow the proppant storage vessel 102 contents to enter the eductor pump assembly 302, and more particularly the suction chamber 318. The suction chamber 318 draws in the continuous proppant output flow 118, including the proppant material 112, as the suction flow, and subsequently mixes with the motive flow, and more particularly, at least a portion of the pressurized fracturing fluid output flow 136. Operation of the apparatus is continuous and uninterrupted with a continuous flow of the proppant output flow 118 and the fracturing fluid output flow 136 in a volume sufficient to provide continuous operation of the apparatus 300 in an uninterrupted episode for each individual fracture stage as desired by the fracture stage plan.

It should be noted that valve mechanism 322 is optional, being required in an application where the desire is to allow the eductor pump assembly 302 to remain at full pressure. As valves in the direct path of the proppant output flow 118, and more particularly proppant material 112, it will be subject to a harsh abrasive environment, it is realized that valve mechanism 322 will be subject to higher wear rates. As such, an embodiment eliminating the valve mechanism 322 is anticipated.

The eductor pump assembly 302 is configured to output a continuous pressurized proppant output flow 122 of a sufficient mass and a continuous pressurized fracturing fluid output flow 136 of a sufficient volume to provide continuous operation of the apparatus 300 in an uninterrupted episode for each individual fracture stage. The apparatus 300 further includes the pressurized blender, or pressurized mixing apparatus, 124 coupled to the eductor pump assembly 302 to continuously receive the discharged continuous pressurized proppant output flow 122 therefrom and the continuous pressurized fracturing fluid output flow 136. The pressurized mixing apparatus 124 is configured to mix the continuous pressurized proppant output flow 122 and the continuous pressurized fracturing fluid output flow 136 therein and output a continuous pressurized fluid mixture (slurry) output flow 138 of proppant and fracturing fluid at the mixing pressure. A fracturing fluid booster pump 141 and a high pressure fracturing fluid (slurry) pump assembly 142 are coupled to the mixing apparatus 124 and configured to deliver the continuous pressurized fluid mixture (slurry) 138 therein to a downstream component 146 as a high pressure fluid mixture (slurry) output flow 148 at an injection pressure, wherein the injection pressure is greater than the mixing pressure, and of a sufficient volume and mass to provide continuous operation of the apparatus 300 in an uninterrupted episode for each individual fracture stage to deliver the proppant mass & fluid volume desired by the fracture stage plan.

Accordingly, the inclusion of the eductor pump assembly 302, as described in apparatus 300, provides for use of at least a portion of the continuous flow of-pressured fracturing fluid 136 as the motive fluid flow through the eductor pump assembly 302 to convey the proppant 112 and more particularly the proppant output flow 118 into the flowing motive fluid.

Referring now to FIG. 5, illustrated is another embodiment of an apparatus for preparing and delivering a continuous fluid mixture (slurry) of solids (proppant) and liquefied gas, generally referenced 400. The apparatus 400 includes a proppant storage vessel 102 configured to contain therein a proppant material 112 and output a continuous proppant output flow 118 at ambient pressure. The apparatus 400 further includes a fracturing fluid storage vessel 128 configured to contain therein a pressurized fracturing fluid 134 and output a continuous pressurized fracturing fluid output flow 136 at or above a mixing pressure, wherein the mixing pressure is greater than the ambient pressure as previously described. A high pressure differential solids feeder assembly 104 is provided and coupled to the proppant storage vessel 102 and the fracturing fluid storage vessel 128. The high pressure differential solids feeder assembly 104 includes a proppant inlet 106 in fluidic communication with the continuous proppant storage vessel proppant output flow 118. In this particular embodiment, the high pressure differential solids feeder assembly 104 is a positive displacement pump, and more particularly a rotary-type positive displacement pump, such as an internal gear, screw, rotary valve, or auger type pump assembly, referenced 402. The unique design of the positive displacement pump 402 ensures that the proppant material 112 is constantly present at a feed inlet 404, while the controlled rotation of a feed mechanism 406 moves the proppant material 112, and more particularly the continuous unpressurized proppant output flow 118, from the ambient pressure feed inlet 404 to a pressurized discharge point 408. In the illustrated embodiment, the feed mechanism 406 comprises a screw mechanism 410 (a helical surface surrounding a central cylindrical shaft) disposed inside a hollow body 412.

As illustrated in FIG. 5, the continuous proppant output flow 118 is initially input into the rotary-type positive displacement pump 402 via the feed inlet 404. Similar to the previous embodiment, the input of the continuous proppant output flow 118 may be metered by an optional valve mechanism (not shown). Similar to the continuous solid feed pump assembly 202 of FIG. 3, the positive displacement pump assembly 402 employs positive-displacement action to feed the proppant material 112 as a free-flowing material with a uniform discharge in a linear volumetric fashion. In contrast to the continuous solid feed pump assembly 202 of FIG. 3, the positive displacement pump assembly 402 employs screws, augers, rotary valves, belts or vibratory trays to convey the proppant material 112 therein. The continuous proppant output flow 118 is initially input at the feed inlet 404 that is coupled to the pump body 412. As the continuous proppant output flow 118 enters and fills the pump assembly 402, and more particularly the pump body 412, the material is carried by the feed mechanism 406 contained therein, toward the discharge point 408. The continuous ambient pressure proppant output flow 118 is rotated within the feed mechanism 406, housed within the pump body 412 and discharged via an output duct 414 at the discharge point 408 as a continuous pressurized proppant output flow 122. At the time of discharge via an outlet 120, the continuous proppant material output flow 122 is output at an increased pressure, and more particularly at a mixing pressure that is greater than the ambient pressure and of a sufficient mass to provide continuous operation of the apparatus 400 in an uninterrupted episode for each individual fracture stage to deliver the proppant mass & fluid volume desired by the fracture stage plan.

In a preferred embodiment, during operation, the proppant material 112 enters the rotary-type positive displacement pump 402 at the feed inlet 404. As the proppant material 112 rotates in the feed mechanism 410 and pump body 412, the pressure of the proppant material 112 is increased. Discharge of the proppant material 112 at the increased mixing pressure occurs upon rotation of the feed mechanism 406 relative to the outlet 120.

The apparatus 400 further includes a pressurized blender, or mixing apparatus, 124 coupled to the rotary-type positive displacement pump 402 to receive the discharged continuous pressurized proppant output flow 122 therefrom and the continuous pressurized fracturing fluid output flow 136. The mixing apparatus 124 is configured to mix the continuous pressurized proppant output flow 122 and the continuous pressurized fracturing fluid output flow 134 therein and output a continuous pressurized flow of a fluid mixture (slurry) 138 of proppant material 112 and fracturing fluid 134 at an increased pressure of a sufficient volume and mass to provide continuous operation of the apparatus 400 in an uninterrupted episode for each individual fracture stage as required by the fracture stage design. A high pressure fracturing fluid (slurry) pump assembly 142 coupled to the mixing chamber 124 is configured to receive the continuous pressurized flow of a fluid mixture (slurry) 138 and deliver a continuous pressurized flow of a high pressure fluid mixture (slurry) 148 to a downstream component 146 at an injection pressure, wherein the injection pressure is greater than the mixing pressure, and of a sufficient volume and mass to provide continuous operation of the apparatus 400 in an uninterrupted episode for each individual fracture stage. In this particular embodiment, a separate booster pump is not provided, and in lieu of, boosting of the mixing pressure is provided as part of the functionality of the high pressure fracturing fluid (slurry) pump assembly 142.

FIG. 6 is a schematic block diagram of a method 500 of delivering a fluid mixture using direct proppant injection to a pressurized mixing apparatus including the high pressure differential solids feeder assembly 100, 200, 300, 400 according to an embodiment disclosed herein. Generally, the method involves providing an input of a proppant material 112 to an ambient pressure proppant storage vessel 102, and providing an input of a pressurized fracturing fluid 134 to a fracture fluid storage vessel 128, at a step 502. Next in step 504, a continuous proppant output flow 118 at ambient pressure from the proppant storage vessel 102 is input into a high pressure differential solids feeder assembly 104. As previously described, the high pressure differential solids feeder assembly 104 may be configured as a positive displacement pump assembly, and more particularly a continuous solid feed pump assembly 202 (as best illustrated in FIG. 3), as an eductor pump assembly 302 (as best illustrated in FIG. 4) or a rotary-type positive displacement pump 402 (as best illustrated in FIG. 5). Next in step 506, a continuous pressurized proppant output flow 122 and a continuous pressurized fracturing fluid output flow 136 are input to a pressurized mixing apparatus 124. The pressurized mixing apparatus 124 is configured to mix the continuous pressurized proppant output flow 122 and the continuous pressurized fracturing fluid output flow 136 therein and output a continuous pressurized fluid mixture (slurry) output flow 138 of the proppant and fracturing fluid at the mixing pressure, at step 508. The pressure of the continuous pressurized fluid mixture (slurry) output flow 138 is next increased in a high pressure fracturing fluid (slurry) pump assembly 142, at step 510. Subsequently a continuous high pressure fluid mixture (slurry) 148 is delivered to one or more downstream components 146, at a step 512, and ultimately may include delivery to a well head.

The apparatus for delivering a fluid using direct proppant injection, as disclosed herein, enables continuous operation of the apparatus at a steady condition in an uninterrupted episode for each individual fracture stage to deliver the proppant mass & fluid volume desired by the fracture stage design. The apparatus by providing continuous pressurized flows of proppant and fracturing fluid into the mixing apparatus eliminates the stop-start operation that must be performed when the volume being held is smaller than the desired amount needed for each individual fracture stage design. The apparatus removes the requirement to store all (or at least a significant portion) of the proppant to be used for each fracturing stage in a pressurized bulk proppant storage pressure vessel, and instead allows use of existing proppant management apparatus at ambient pressure such that an unlimited amount of proppant can be blended online (as opposed to in batches) with the pressurized fracturing fluid to deliver the proppant mass and fluid volume desired by the fracture stage design.

Additional commercial advantages of the disclosed apparatus are related to the current problem faced in unconventional gas development and the requirement to mix/blend chemicals and a proppant, namely sand with fracturing fluids (e.g., liquid CO₂, liquid propane gas) that require they always be contained at a suitable mixing pressure to avoid vaporization of these fracturing fluids. Accordingly, disclosed is an apparatus and method of continuously preparing and delivering a fluid mixture of solids (proppant) with liquefied gas using a high pressure differential solids feeder assembly and direct proppant injection into a pressurized mixing apparatus in such a way that a continuous pressurized flow of proppant of a sufficient volume to provide continuous operation of the apparatus in an uninterrupted episode for each individual fracture stage can be provided without being constrained by the total volume limits of the known lock hopper based approaches. The disclosed apparatus provides a continuous pressurized fluid mixture output flow of a sufficient volume and mass to provide continuous operation of the apparatus in an uninterrupted episode for each individual fracture stage to deliver the proppant mass and fluid volume desired by the fracture stage design.

The foregoing has described an apparatus and method of preparing and delivering a fluid mixture (slurry) of solids (proppant) and liquefied gas using direct injection of a proppant into a pressurized mixing apparatus. While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. While the present disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the disclosure. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. 

1. An apparatus for preparing and delivering a fluid mixture, the apparatus, comprising: an unpressurized proppant storage vessel configured to contain a dry proppant material at an ambient pressure and output a continuous unpressurized proppant output flow at the ambient pressure; a fracturing fluid storage vessel configured to contain a pressurized fracturing fluid and output a continuous pressurized fracturing fluid output flow at a fracture fluid mixing pressure; a high pressure differential solids feeder assembly coupled with the unpressurized proppant storage vessel and the fracturing fluid storage vessel to output a continuous and uninterrupted flow of pressurized proppant output, wherein the high pressure differential solids feeder assembly comprises an eductor pump assembly, a converging-diverging nozzle, and Venturi enabling conversion of a pressure energy at a first portion of motive flow of pressurized fracturing fluid to a velocity energy, enabling the dry proppant material to be drawn out of the unpressurized proppant storage vessel and then to be injected into a pressurized mixing apparatus coupled with the high pressure differential solids feeder assembly.
 2. The apparatus of claim 1, wherein the continuous and uninterrupted flow of pressurized proppant output comprises output of a sufficient mass to achieve a continuous and uninterrupted operation of the apparatus for an individual fracture stage, and the output of the continuous and uninterrupted flow of pressurized proppant output is at the mixing pressure.
 3. The apparatus of claim 1, wherein the mixing pressure is greater than the ambient pressure and further wherein the continuous pressurized fracturing fluid output flow is split into the first portion and a second portion.
 4. The apparatus of claim 3, wherein the first portion is input into the pressurized mixing apparatus through the converging-diverging nozzle and the Venturi.
 5. The apparatus of claim 3, wherein the second portion is input directly into the pressurized mixing apparatus.
 6. The apparatus of claim 1, wherein the pressurized mixing apparatus comprises at least one inlet in fluidic communication with the continuous pressurized proppant output flow and at least one inlet in fluid communication with the second portion of the continuous pressurized fracturing fluid output flow at the mixing pressure.
 7. The apparatus of claim 1, wherein the high pressure differential solids feeder assembly comprises a proppant inlet to input the continuous unpressurized proppant flow at the ambient pressure into the high pressure differential solids feeder assembly and a fracture fluid inlet to input the first portion of the continuous pressurized fracturing fluid output flow into the high pressure differential solids feeder assembly as the motive flow.
 8. The apparatus of claim 1, wherein the pressurized mixing apparatus comprises a tank, the tank comprising a mixer to mix the continuous pressurized proppant output flow and the continuous pressurized fracturing fluid flow in the pressurized mixing apparatus.
 9. The apparatus of claim 8, wherein the mixer comprises at least one of plates and mixer elements.
 10. The apparatus of claim 8, wherein the mixer mixes the continuous pressurized proppant output flow and the continuous pressurized fracturing fluid flow in the pressurized mixing apparatus by at least one of agitation and static mixing.
 11. The apparatus of claim 1, wherein the pressurized mixing apparatus provides an output of a continuous and uninterrupted flow of a pressurized fluid mixture of proppant and fracturing fluid of a sufficient volume and mass to achieve continuous operation of the apparatus in an uninterrupted episode for the individual fracture stage, wherein the continuous and uninterrupted flow of the pressurized fluid mixture of proppant and fracturing fluid is output at or above the mixing pressure.
 12. An apparatus for preparing and delivering a fluid mixture, the apparatus, comprising: an unpressurized proppant storage vessel configured to contain a dry proppant material at an ambient pressure and output a continuous unpressurized proppant output flow at the ambient pressure; a fracturing fluid storage vessel configured to contain a pressurized fracturing fluid and output a continuous pressurized fracturing fluid output flow at a fracture fluid mixing pressure, wherein the mixing pressure is greater than the ambient pressure and further wherein the continuous pressurized fracturing fluid output flow is split into a first portion and a second portion; and a high pressure differential solids feeder assembly coupled with the unpressurized proppant storage vessel and the fracturing fluid storage vessel to output a continuous and uninterrupted flow of pressurized proppant output, wherein the high pressure differential solids feeder assembly comprises an eductor pump assembly, a converging-diverging nozzle, and Venturi enabling conversion of a pressure energy at the first portion of motive flow of pressurized fracturing fluid to a velocity energy, enabling the dry proppant material to be drawn out of the unpressurized proppant storage vessel and then to be injected into a pressurized mixing apparatus coupled with the high pressure differential solids feeder assembly, wherein the pressurized mixing apparatus comprises at least one inlet in fluidic communication with the continuous pressurized proppant output flow and at least one inlet in fluid communication with the second portion of the continuous pressurized fracturing fluid output flow at the mixing pressure.
 13. An apparatus for preparing and delivering a fluid mixture, the apparatus, comprising: an unpressurized proppant storage vessel configured to contain a dry proppant material at an ambient pressure and output a continuous unpressurized proppant output flow at the ambient pressure; a fracturing fluid storage vessel configured to contain a pressurized fracturing fluid and output a continuous pressurized fracturing fluid output flow at a fracture fluid mixing pressure; and a high pressure differential solids feeder assembly coupled with the unpressurized proppant storage vessel and the fracturing fluid storage vessel to output a continuous and uninterrupted flow of pressurized proppant output, wherein the high pressure differential solids feeder assembly comprises an eductor pump assembly, a converging-diverging nozzle, and Venturi enabling conversion of a pressure energy at a first portion of motive flow of pressurized fracturing fluid to a velocity energy, enabling the dry proppant material to be drawn out of the unpressurized proppant storage vessel and then to be injected into a pressurized mixing apparatus coupled with the high pressure differential solids feeder assembly, wherein the high pressure differential solids feeder assembly comprises a proppant inlet to input the continuous unpressurized proppant flow at the ambient pressure into the high pressure differential solids feeder assembly and a fracture fluid inlet to input the first portion of the continuous pressurized fracturing fluid output flow into the high pressure differential solids feeder assembly as the motive flow, further wherein the pressurized mixing apparatus comprises a tank, the tank comprising a mixer to mix the continuous pressurized proppant output flow and the continuous pressurized fracturing fluid flow in the pressurized mixing apparatus. 